The present disclosure relates to fluid flow measurement systems. Measuring the velocity of fluid flows is essential for countless applications, many of which including those in the gas, oil, and nuclear fields, require systems which can be used in highly corrosive environments and which have minimal maintenance requirements.
Previously described methods of measuring fluid flow include pressure-based systems that restrict fluid flow in order to measure its rate from the resulting pressure difference, or mechanical methods that rely on a moving mechanical apparatus (e.g. a pinwheel, rotor, or the like) placed in the fluid stream. Other previously described methods include vortex flow meters, wherein a bluff body is placed in the path of the fluid. Vortices are created as the fluid passes the bluff body. The vortices trail behind the bluff body and the frequency of the vortex shedding off the bluff body is detected, often via a piezoelectric crystal or other sensor, which produces a small, but measurable, voltage pulse each time a vortex is created. The frequency of the pulse is measured and the fluid flow velocity is calculated by V=f L/S where f is the frequency, L is the characteristic length of the bluff body. And S is the Strouhal number, which is essentially a constant for a given body shape within its operational limits. Still further methods of measuring flow rates include optical flow meters which typically measure the actual speed of particles in the fluid flow. In this instance small particles in the fluid pass through two laser beams spaced a known distance apart from each other. A signal is generated when a particle passes through the first laser beam and a second signal is generated when the same particle passes through the second laser beam. Fluid flow velocity is calculated by V=D/T where D is the distance between the laser beams and T is the interval between the generation of the first and second signals. All of these existing methods have limitations. Restriction of the flow rate can be detrimental to a given system or process, while mechanical flow measurement devices are sometimes less restrictive to the flow itself, but their moving parts can fail. Previously described vortex flow meters may rely on expensive sensors and electronics that may be destroyed is corrosive environments and previously described optical flow meters that rely on the ability to detect the same particle passing through different laser beams may be expensive or impractical in various environments. Accordingly, there remains a need for inexpensive fluid flow measurement systems which can be used in chemically harsh environments and which require minimal to no maintenance.